Assuming that the electric service connection to the motor home at 
Tom's camp site is up to code, an AC supply plugged into an outlet 
inside the motor home will be grounded to the service ground, just as 
it would inside a house.

So, a wire between the ground screw on the radio and the ground screw 
on the power supply would also tie the radio to the service ground.

While that is a good electrical ground, it may not be good for RF.

However, as has already been said, he will probably not have an RF 
problem due to the type of antenna.

If he does, the old coil of coax trick should solve that problem if he 
doesn't already have a 1 to 1 ballun, or a line isolator.

-- 
Mike Duke, K5XU